U.S. Pat. No. 5,611,281 issued Mar. 18, 1997 to Corrado et al., which is hereby incorporated by reference, discloses a system for axially reciprocating a tacky roller (also referred to herein as a contact cleaning roller, or “CCR”) across a substrate being cleaned by the roller. Such reciprocation is useful for spreading particles which may be non-uniformly distributed on the substrate surface over a broader area of the CCR collecting surface, thereby decreasing the rate of decay of collecting efficiency, improving the average cleanliness of the treated substrate, and extending the operating lifetime of the CCR between renewals. In the prior art, the CCR is mounted in a movable frame which is journalled in linear bearings and is displaceable axially of the shaft by a controllable actuator.
To avoid scratching or scrubbing of the substrate surface by the CCR while the roller is simultaneously rolling along the surface in a first direction and axially sliding across the surface in a second and orthogonal direction, the rate of axial displacement is preferably very low; that is, the ratio of axial to rotational linear velocities is preferably between about 0.01 and about 0.0001. In practice, therefore, the reciprocating actuator may be required to operate at about 1 cycle per minute (cpm) or even less. It can be expensive and difficult to provide an actuating system having the capability for such smooth, slow motion. Such a system may require an actuator, air or hydraulic supply, and an electronic controller having this capability. In addition, such a system is subject to unwanted variation from misadjustment, wear, and drift in electronic and pneumatic components.
A mechanical system for smoothly oscillating a roller is disclosed in U.S. Pat. No. 5,855,172 issued Jan. 9, 1999 to Corrado et al., which is hereby incorporated by reference. The improved system comprises a shell having an electrostatically active outer surface, the shell being supported by a close-fitting rotatable shaft. The shaft within the shell is provided with a spiral cam groove extending from a first axial location to a second axial location disposed 180° from the first axial location, and then back to the first axial location. A cam follower attached to the inner surface of the shell rides in the cam groove, causing the shell to oscillate axially of the shaft at a frequency of oscillation which is the numerical difference between the rotational frequencies of the shell and shaft. Preferably, the shell is nipped against a backing roller, which may be an idle roller or a driven roller with a moving web substrate passing therebetween in contact with the working surfaces of both rollers. Outboard of the working surfaces, the shaft of the backing roller has a first drive roller having a first diameter, and the shaft of the barrel cam has a second drive roller nipped against the first drive roller and having a second roller diameter slightly different from the first roller diameter. Thus, the shell turns at a rotational frequency imposed by the linear velocity of the web substrate whereas the shaft turns at a different frequency as imposed by the relative diameters of the two speed-controlling drive surfaces, the frequency differential being equal to the oscillation frequency of the shell along the barrel cam.
A shortcoming of the prior art barrel cam system is that the mechanism that ratios the rotational rates of the shell and the barrel cam is rather cumbersome, requiring a roller pair that extends beyond the limits of the roller shell and includes a drive gear supported by the backing roller, and thus cannot be contained within the shell. Further, the mechanism cannot be contained largely within an axial envelope extension of the shell, making the apparatus unsuited to compact installations such as a “drawer slide” configuration.
What is needed in the art is a compact barrel cam arrangement that can be contained within a roller shell or largely within the axial envelope extension thereof.
It is a principal object of the present invention to provide a compact barrel cam system that can axially oscillate a roller rolling along a moving substrate surface.